Method of producing copper having high electrical conductivity and being free from oxygen



Patented Feb. 18, 1936 UNITED STATES PATIENT OFFICE METHOD OF PRODUCING COPPER HAVING HIGH ELECTRICAL CONDUCTIVITY AND BEING FREE FROM OXYGEN Hermann von Forster and Fritz Kiinstel, Frankfort-on-the-Main,

Germany, assig'nors American Lurgi Corporation, New York, N. Y.

No Drawing. Application June 22, 1935, Serial No. 27,872. In Germany June 27, 1934 9 Claims. (01. 75- 62)- The present. invention relates to a method of producing copper having high electrical conductivity and being free from oxygen.-

It is well known that copper which is completely free from oxygen and other gases has surprisingly excellent properties even in a cast condition. Thus, oxygen-free copper has been sold produced from. D. 0. copper has considerable advantages over the conventional copper wire as may be appreciated from the fact that the torsion values of 2 mm. wires are to each other as 100 is to 50. Due to the advantages of D. 0.

copper, many attempts have been made to produce such copper. The usual refining process cannot be used due to the fact that when an attempt has been made to carry the deoxidation beyond the customary degree excessive amounts of gases have been introduced into the copper which makes it impossible to cast satisfactory ingots. Proposals have been made to degasify copper by vacuum, but such a procedure involved the installation of expensive equipment and generally prevented the use of smelting equip.-

ment usually available at refineriesf Vacuum' processes for producing copper have been described in British Patent No. 378,008 and have required the use of an electric furnace to carry the reduction up to the necessary excessive pointwhile under vacuum. Attempts have been made to deoxidize and/or desulfurize copper as may be,

seen from German Patent No. 4'71,209 and U. S. Patent No. 1,812,992 and to free copper from nitrogen or from excess of phosphorus as may be seen from U. S. Patent No. 1,812,993. Other investigators have proposed preventing oxygen from having access to the molten copper at the time of casting. Such a proposal has been described in British Patent No. 378,008. Various other proposals have been made, but they have had shortcomings, defects and disadvantages of one sort or another. been confronted witha vexatious and diflicult problem of producing oxygen-free copper of The copper industry has.

We have discovered a relatively simple and practical process of producing oxygen-free copper of high electrical conductivity which can be carried into practice in an ordinary copper refinery with the customary equipment.

It is an object of the invention to provide a 5 process for producing oxygen-free copper of high electrical conductivity which is economical and which can be conducted in a satisfactory manner on an industrial scale to produce a conmqercially acceptable product.

The present invention also contemplates the provision of a' unique combination'of operations to produce a high grade, oxygen-free copper .of high electrical conductivity.

A further object of the present invention is to provide a process of producing oxygen-free copper of high conductivity including an opera- 'tion which has heretofore been considered as highly detrimental and which has heretofore always produced a defective copper which was unacceptable to'the trade and which could not be sold.

It is another object of the invention to provide a process of producing oxygen-free copper of high electrical conductivity which involves the use of pre-glown charcoal to prevent access of air to the molten copper and to eliminate the reabsorption of gas by the copper.

Other objects and advantages will become apparent from the following description.

According to the present invention, we have discovered that overpoling can be used to bring about new results and can be successfully employed to produce oxygen-free copper of high conductivity and of good physical properties. Our discovery is in direct contrast to the belief of the art that overpoling copper is harmful and to the experience of the'art that overpoled copper is a defective product. As a matter of fact, it has become practice of copper refineries to use great care and to prevent overpoling. When copper was overpoled and the oxygen content of the copper was reduced below about 0.025% to about 0.07%, the overpoled copper had to be completely retreated again and had to be re-blown with air to oxidize the entire melt of copper before attempting to re-pole to an oxygen content of about 0.025% to about 0.07%.

In accordance with the present invention, cop per is first treated in the usual refining furnace and is freed from impurities by blowing air through the melt in the manner. The oxygen absorbed by the molten copper is removed by 'poling. By proceeding in accordance with.

the principles of the present invention, the copper melt is deliberately and intentionally overpoled to reduce the oxygen content far below the standard limits heretofore employed and to an profit. Heretofore, prior processes required such a relatively large amount of lithium or lithiumcontaining material as to be commercially pro-'- hibitive due to the high price of lithium. The

present process eliminates this vitally objectionable aspect of using lithium in the treatment of copper. I

Due to the strong tendency of molten copper to absorb air (oxygen), special precautions must be taken to prevent the absorption of oxygen, particularly during the teeming from the furnace to the ladle and during the casting from the ladle to the ingot mold. We have found a very practical process for preventing access of air to the copper melt and for preventing the re-absorption of gases even of a reducing character'which have heretofore been used to provide a reducing atmosphere over the copper melt. By using a solid of reducing character which has been specially prepared, we have been able to obtain novel and unexpected results and to provide a reducing atmosphere over the copper melt while eliminating or reducing to a minimum the reabsorption of gases by the copper. The treating der is carried away by the convection currents (streams of air, etc.) produced above the molten copper. Our experiments/have shown that a grain size of about 2 to about 6 mm. gives the best results. When uslng'charcoal having the aforesaid grain size, the individual grains will come close enough to each other to completely exclude the admission of fresh air to the charcoal. but the grains are large enough to prevent them from being driven upwards by means of a hot gas column above the bath of molten copper.

The glowing is preferably can'ied out in such a manner that the charcoal which has been in stock is ignited in small quantities. -After burning the charcoal for several hours, the glowing has progressed sumciently and the charcoal is completely degaaifiedi In this condition, the pre-glowed charcoal can be immediately used for covering the molten copper. 1

For the purpose of giving those skilled in the art a better understanding of the invention, the

following illustrative example will now be described.

Electrolytic copper in the form of a cathode is melted in a refining furnace in the usual manner. By blowing air through and into the molten copper, the latter will be enriched with oxygen and the impurities contained in the cathodes such as hydrogen and sulfur compounds including sulfuric acid, are driven out. Thereafter, the copper is poled by means of poling stems, whereby the oxygen content of the copper. which was increased by means of the blowing of air to 0.8%, is reduced to about 0.03 to about 0.06%. This is the oxygen content at which copper is cast according to the usual refining process, and which, according to conventional processes, is removed by means of special deoxidizing agents such as phosphorus, calcium, lithium or thelike. In contrast to prior processes, the present invention contemplates carrying the deoxidizing to an accentuated degree by means of over-poling. Thus, the overpollng is continued until the oxygen content is reduced below about 0.01%, say, for example, to about 0.005%. In the usual processes the poling is not continued that far, because simultaneously with the removal of oxygen, poling gases (such as, H2,CO, light hydrocarbons, etc.) are dissolved by the copper and produce a porous structure after solidification. According to the present invention, the dissolution of these gases is permitted because it has been discovered that the excess of poling gases may be easily rendered harmless by means of lithium. As soon as the copper is reduced to an accentuated low oxygen content, which occurs at a temperature of about 1130 C. to about 1150" C., the copper is cast into a ladle in which pre-glowed charcoal comminuted to about 2 to about 6 mm. prevents the contact of the copper with'the air. When molten copper is filled in the ladle; about 0.012 to about 0.015% lithium is introduced. The introduction of lithium is preferably carried out by using lithium in metallic form and by inserting the lithium into the copper melt by means of a pointed copper bar having small quantities of lithium (about 30 to about 50 grams) on its point and by dipping the end of this bar into the bath. Accordingly, about 250 grams of lithium are introduced into a casting ladle containing about 2000 kg. of copper in 5 or 6 successive operations, preferably by dipping-deeply into the copper bath in order to keep the lithium. This is accomplished so rapidly that.

immediately after the introduction of the last amount of lithium the copper may be cast.

The casting is carried out in such a manner that the copper is cast directly from the ladle into upright ingot molds filled with a reducing or with a neutral gas, such as carbon monoxide, etc. The jet of copper falling from the ladle into the mold is surrounded by the aforesaid gas. The copper treated in such a manner will have a depression on its surface after solidification, which is caused by shrinkage. For this reason, the head of the ingots has to be sewn oil prior to their practical use and application; It has been found that it is possible to fill out the shrinkage cavity by casting into same copper pre-treated in the same manner. Copper treated in such a manner does not show any protoxide in the micro-photograph, so that it may be assumed that the oxygen content is practically zero. Lithium is only present as a trace in copper produced by the present process.

The electrical conductivity of comic produced by the present process is just as high as that of customary wire bars. However, the mechanical properties are much better. For example, the impact value is increased to about 13 meterkiloram/mm in contrast to about 2 to 3 meterkilogram/mm of the usual wire bar; the torsion number of a 3 mm. wire is increased to 100-120 only down to below 0.02% and to use a little more.

lithium for deoxidizing the rest of the oxygen.

It is to be observed that the present process has the great'advantage that it may be carried out in refining furnaces capable of handling many tons of metal without detrimentally influencing the electrical properties of the product.

It is also to be noted that by the present invention, the lithium may be added either in the refining furnace or in a casting ladle. 0f special importance are the steps which are essential for maintaining the copper in the condition of great purity and freedom from gases. For this reason, contact of the copper with-the air or moisture or other substances giving off gases must be prevented. It is not enough to cover the castingladle with coarse charcoal, but the copper has to be covered with comminuted and preglowed charcoal. What is meant, however, is not that the charcoal glows due to its contact with molten copper as has been done before, but the pulverized charcoal has to be ignited a few hours before and the charcoal must be used in a glowing condition for covering the molten copper in a casting ladle or trough.

Furthermore, the present invention involves a process of refining copper which makes it possible to obtain high quality products by means of conventional refining equipment and which has accomplished really remarkable progress.

Moreover, in view of the rapid development of technique, there cannot be the slightest doubt that wide fields of applications are open for copper produced by the present process. For example, oscillation phenomena in the construction of machines and the notch effects in screw joints have an ever increasing importance. In the manufacture of tubes, the possibility of bending by means of welding burners is of great importance. Riveting is more and more replaced by means of welding in the case of copper, for example, in the casev of fireboxes of railroad engines.

In all of these cases, it is of great importance that the copper employed should have the highest possible bending value, torsional strength and notch toughness. The quantity of lithium used by the present process is not excessive. For example, for an overpoled copper produced according to the present invention only 125 grams of lithium per ton of copper have been used. This makes the use of lithium, even at the present high price, commercially possible.

We claim: 1

1. The method of producing practically oxygenfree copper having high electrical conductivity which comprises blowing air into molten copper to remove impurities, overpoling the thus-treated molten copper to reduce the oxygen content to an accentuated degreeto produce practically oxygenfree and sulfur-free copper, treating such copper with a lithium-containing material. to remove gases therefrom, and casting the degasifled practically oxygen-free and sulfur-free copper while preventing the access of air.

2. The method of producing practically oxygenfree copper having high electrical conductivity which comprises overpoling molten copper to an accentuated degree of about 0.003 to 0.01% of oxygen, degasifying the practically oxygen-free and sulfur-free copper by means of lithium, and casting said copper while preventing access of air.

3. The method of producing practically oxygenfree copper having high electrical conductivity which comprises overpoling molten copper to an accentuated degree of about 0.003 to 0.01% of oxygen, degasifying the practically oxygen-free and sulfur-free copper by means of lithium, and casting said copper while preventing access of air by means of pulverized pre-glowed charcoal.

4. The method of producing practically oxygenfree copper having high electrical conductivity which comprises blowing air into molten copper to remove impurities, overpoling the thus-treated molten copper to reduce the oxygen content to an accentuated degree less than about 0.02% to produce practically oxygen-free and sulfur-free copper, treating such copper with a lithium-containing material to remove gases therefrom, and casting the degasified practically oxygen-free and sulfur-free copper while preventing the access of air.

5. The method of producing practically oxygenfree copper having high electrical conductivity which comprises blowing air into molten copper to remove impurities, overpoling the thus treated molten copper to reduce the oxygen content to an accentuated degree to about 0.01% to about,

0.005% to produce practically oxygen-free and sulfur-free copper, treating such copper with a lithium-containing material to remove gases therefrom, and casting the degasified practically oxygen -free and sulfur-free copper while preventing the access of air.

6. The method of producing practically oxygenfree copper having high electrical conductivity which comprises blowing air into molten copper to remove impurities, overpoling the thus treated molten copper to reduce the oxygen content to an accentuated degree to produce practically oxygenfree andsulfur-free copper, treating such copper with a lithium-containing material to remove gases therefrom, and casting the degasified practically oxygen-free and sulfur-free copper while preventing the access of air by means of finely comminuted and pre-glown charcoal.

free copper having high electrical conductivity which comprises blowing air into molten copper to remove impurities, overpoling the thus treated molten copper to-reduce the oxygen content toan accentuated degree to produce practically oxygenfree and sulfur-free copper, treating such copper with a lithium-containing material to remove gases therefrom, and casting the degasified practically oxygen-free and sulfur-free copper while preventing the access of air by means of finely comminuted'and pre-glown charcoal having a grain size of about 2 to about 6 mm.

8. The method of producing practically oxygenfree copper having high electrical conductivity which comprises overpoling molten'copper to an accentuated degree to produce practically oxygenfree and sulfur-free copper, treating said practically oxygen-free and sultur-iree copper with lithium to remove gases therefrom, applying finely comminuted and glowing charcoal to said molten copper, and casting said molten copper. 4

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